Overall, I was indifferent.I'm somewhat skeptical of how much a Watchmen newcomer would grasp in terms of plot, purely because in the Watchmen book, everything is plot, even the pirate story interludes, so to remove one small detail is to remove a trail of breadcrumbs that will end up becoming hugely important. Int his way, Watchmen shares the same problem with the Harry Potter books; namely that genre books thrive on such small details, whereas films are all about the main thrust of narrative, rather than the nice digression about someone's favourite comb which becomes a hugely relevant plot twist.
Foolishly, I have left my copy of Watchmen at my parents' house and I'm not sure when I'm returning there, so comparisons are from memory alone.
The best part was the opening sequence; a beautifully shot overview of fifty years of superhero history, to The Times They Are A-Changin'. I cried. I was moved, people! There was something about seeing the small details of the supporting characters (especially The Silouhette) acknowledged which made me incredibly proud that Watchmen (book) was ever created. This is probably the closest I'll ever get to patriotism.This sequence made me so incredibly hopeful - it completely fulfils the spirit of the book.
Of course, it was all downhill from there. My main problem is with how incredibly glossy everything is; the costumes are suave, the fights are spectacular (and ridiculously violent) - a piece of reflexive metafiction on comicbooks has been turned into everything it isn't supposed to be. These aren't people with preposterous backstories and superpowers; these are strange people who, for their own reasons, made their own costumes, went out into the street and fought crime. And as a result they fucked up their backs and their lives.
The reason why Watchmen worked so well was because the world of the superhero was portrayed as mundane. Their lives were small, and any glory they gained (with a few exceptions) was minimal. And I feel the film didn't manage to grasp that sadness. Even in the character of Dan, an over-weight impotent middle-aged man, the sadness and emptiness of the post-superhero life wasn't really there. Because why linger on that when you can have SUPERCOOL AWESOME FIGHT SCENES!!!!! Ones which I found to be deeply unnecessarily violent. Obviously a super-hero film is going to be violent; I don't expect everyone to be running around with walkie-talkies. But what Zack Snyder has done is strewn blood everywhere, as if blood equates with pain. It doesn't.
This is especially notable in Rorschach's back-story. Film - Rorschach is taunted about his mother's prostitution by an older boy. He jumps on him and bites his ear, blood everywhere. Book: Rorschach is taunted about his mother's prostitition by an older boy. He takes the boy's cigarette and stubs it out in his eye. Which is more disturbing? Even Rorschach's final snapping, when he kills the kidnapper of a young girl has been changed, not to be anymore chilling but bloodier. Film - Rorschach chains the kidnapper to a pipe, takes the butcher's knife used to dismember the little girl and hits the man in the head, for long after he is dead. Book: Rorschach chains the kidnapper to a pipe, places lighter fluid around him and sets fire to the house, leaving as the man screams. Which is more disturbing?
In terms of the changed ending, I was ok with it. It tied the plot to varying other elements earlier, about Doctor Manhattan's power being demonstrated and the fear that he was causing cancer in humans. To have left the original ending in without the varying subplots regarding the organisation of it would have been confusing and pointless.
But the most disappointing part for me, was the subplot between Laurie, her mother and the Comedian. This is the thematic heart of the book, pulling the past and present strands of the plot together, and the main emotional arc, producing the central revelation (aside from the whole giant squid nuking new york thing). it's pretty clear by the placing of this moment in the comic book (the final thing to occur before the Arctic show-down) that this is a very important. And yet, although Laurie's storyline exists in the film, it doesn't have the same impact because Laurie as a character simply isn't there. Gone is the tough chain-smoking woman who is far more like her mother than she is willing to admit, replaced by some who is very annoyed that her boyfriend works so much. There is little or no mention that this is a woman who has spent her life in two roles she wasn't very interested in (superhero and superhero's girlfriend), and is considering how to make a new life for herself. Her tense relationship with her mother is barely there; this is because all the stuff about her childhood is relegated to two small moments where Dr. Manhattan makes her see things with some vague mutterings about her dwelling on the negative side of life. Essentially, Laurie becomes the very sex symbol and superhero girlfriend she was created to invert.
Not to mention the costume. Somehow, a leotard and a filmy skirt became a pvc catsuit/corset with suspenders and spike heels. Laurie laughs about how ridiculous her costume was, whilst the camera zooms in on her arse in said costume. Not so much having your cake and eat it as having a whole fucking bakery.